Many devices used in biomedical applications require that the bulk of the devices have one property and the surfaces of the device have a different property. For example, contact lenses may require relatively high oxygen permeability through the bulk of the lens to maintain good corneal health. However, materials that exhibit exceptionally high oxygen permeability (e.g. polysiloxanes) are typically hydrophobic and, will up take lipid or protein from the ocular environment and may adhere to the eye if not treated or surface-modified. Thus, a contact lens will generally have a core or bulk material that is highly oxygen permeable and hydrophobic, and a surface that has been treated or coated to increase hydrophilic properties. This hydrophilic surface allows the lens to move relatively freely on the eye without absorbing excessive amounts of tear lipid and protein.
In order to modify the hydrophilic nature of a relatively hydrophobic contact lens material, a coating may be applied onto the surface of a contact lens using a number of technologies, including a plasma treatment process (e.g., PCT Publication Nos. WO 96/31793, WO 99/57581, WO 94/06485), a Langmuir-Blodgett deposition process (e.g., U.S. Pat. Nos. 4,941,997; 4,973,429; and 5,068,318), a controlled spin casting process, a chemisorption process, a vapor deposition or a layer-by-layer polymer adsorption process that is preceded by a charge inducing process. These techniques are not cost-effective and are difficult to be implemented in an automated production process.
Another coating technique is a layer-by-layer (“LbL”) polyelectrolyte absorption process. For example, Yoo, et al. reported a process which involves alternatively dipping hydrophilic glass substrates in a polyelectrolyte solution (e.g., polycations such as polyallylamine or polyethyleneimine) and then in an oppositely charged solution to form electrically conducting thin films and light-emitting diodides (LEDs) (Yoo, et al., “Investigation of New Self-Assembled Multilayer Thin Films Based on Alternately Adsorbed Layers of Polyelectrolytes and Functional Dye Molecules”, Mat. Res. Soc. Symp. Proc. 413: 395400 (1996)).
A series of three articles described similar LbL polyelectrolyte absorption processes (Ferreira & Rubner, Macromolecules, 28: 7107-7114 (1995); Fou & Rubner, Macromolecules, 28: 7115-7120 (1995); and Cheung et al., Macromolecules, 30:2712-2716 (1997)). These processes involve treating glass substrates that have hydrophilic, hydrophobic, negatively, or positively charged surfaces. The glass surfaces are treated for extended periods in hot acid baths and peroxide/ammonia baths to produce a hydrophilic surface. Hydrophobic surfaces are produced by gas-phase treatment in the presence of 1,1,1,3,3,3-hexamethyldisilazine for 36 hours. Charged surfaces are prepared by covalently anchoring charges onto the surface of the hydrophilic slides. For example, positively charged surfaces are made by further treating the hydrophilic surfaces in methanol, methanol/toluene, and pure toluene rinses, followed by immersion in (N-2 aminoethyl-3-aminopropyl) trimethyloxysilane solution for 12 to 15 hours. This procedure produces glass slides with amine functionalities, which are positively charged at a low pH.
U.S. Pat. Nos. 5,518,767 and 5,536,573 to Rubner et al. describe methods of producing bilayers of p-type doped electrically conductive polycationic polymers and polyanions or water-soluble, non-ionic polymers on glass substrates. These patents describe extensive chemical pre-treatments of glass substrates that are similar to those described in the aforementioned articles.
U.S. Pat. No. 5,208,111 to Decher et al. describes a method for applying one or more layers to a support modified by the applications of ions and ionizable compounds of the same charges over the entire area. The one or more layers are made of organic materials which in each layer contain ions of the same charge, the ions of the first layer having the opposite charge of the modified support and in the case of several layers each further layer having again the opposite charge of the previous layer.
U.S. Pat. No. 5,700,559 to Sheu et al. discloses a method for making a hydrophilic article having a substrate, an ionic polymeric layer bonded directly onto the substrate, and a disordered polyelectrolyte coating ionically bonded to the ionic polymeric layer. The ionic polymeric layer is obtained by a plasma treatment, an electron beam treatment, a corona discharge, an X-ray treatment, or an acid/base chemical modification of the substrate.
Although each of these surface modification techniques are effective for producing an article with a surface that is different from the remainder of the article, the modification processes requires complex and time-consuming pretreatment of the substrate surface. To overcome this problem, various layer-by-layer (LbL) polyelectrolyte deposition techniques have been developed by the assignee of the present invention (e.g., PCT Publication Nos. WO 01/57118, WO 99/35520). These layer-by-layer techniques effectively alter the surfaces of various materials, such as contact lenses. One layer-by-layer (LbL) coating technique involves consecutively dipping a substrate into oppositely charged polymeric materials until a coating of a desired thickness is formed. In addition, another technique that results in a layer-by-layer coating while avoiding the time-consuming aspects of sequential dipping, is the single dip process disclosed in co-pending U.S. Patent Application Ser. No. 60/180,463 filed on Feb. 4, 2000, entitled “Single-Dip Process for Achieving a Layer-by-Layer-Like Coating”, which applies charged polymeric material onto the substrate with only a single dip. In this technique, a generally hydrophobic article such as a contact lens is dipped into a single charged polymeric solution containing at least one polycationic material and at least one polyanionic material. The polycationic material may include a positively charged moiety such as poly(allyl amine hydrochloride) and the polyanionic material may include a negatively charged moiety such as polyacrylic acid. Typically, the charged polymeric components are employed in non-stoichometric amounts such that one of the components is present within the solution in a greater amount than another component.
Each of these LbL-coating techniques is effective for producing an article with a surface that is different from the remainder of the article. However, these LbL-coating techniques require at least two oppositely charged polymeric materials and an article having an LbL coating produced therefrom may have a highly charged surface. A contact lens having a highly charged surface may be susceptible to the depositions of some proteins on the lens surface and/or may cause undesirable adverse effects on the wearer's comfort and/or ocular health. Therefore, it would be desirable if an LbL-coating process can be developed to produce coated articles having a significantly decreased charge density.